Automatic traction control for friction drives

ABSTRACT

The disclosure relates to improved friction drive systems, control algorithms for friction drive systems, and automatic traction control for friction drive systems. Embodiments of friction drive systems and methods may improve control over an amount of normal force between a contact surface on a friction drive (e.g., disposed on a drive motor) and a tire or wheel of a wheeled vehicle. Embodiments of friction drive systems and methods may dynamically adjust the normal force between the contact surface and the tire or wheel in response to rapidly changing conditions, such as weather, road surface, and/or tire inflation. Embodiments of an automatic traction control system may adjust the normal force to avoid slippage while minimizing tire wear and maximizing battery efficiency. Embodiments of friction drive systems and methods may allow a user to calibrate or adjust the amount of normal force delivered based on their preferences or based on a selected mode of operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/243,661, filed on Oct. 19, 2015, which is herebyincorporated by reference in its entirety.

FIELD OF INVENTION

The inventions disclosed herein relate to the field of friction drivesystems, including friction drive systems that are capable of poweringwheeled vehicles such as bicycles, scooters, wheelchairs, skateboards,strollers, wagons, tricycles, and other human powered vehicles. However,the inventions disclosed herein have applications beyond wheeledvehicles and may also be used with other devices, such as motorcycles,remote control vehicles, robots, wind turbines, manufacturing systems,conveyor belts, railcars, trains, printers, toys and consumer devices,among others.

BACKGROUND

Friction drive systems for powering wheeled vehicles, such as bicycles,have existed for many years. These systems deliver power through directcontact with the wheel or tire of the vehicle. Typically, a motor ismounted in a fixed position adjacent to one of the wheels. The motor canthen either drive the wheel through a secondary roller mechanism pressedagainst the tire or directly via tire contact with the rotating outershell of an outrunner-type motor.

A contact surface on the rotating mechanism of the friction drivepresses against the tire, thereby delivering mechanical power to thewheel. Friction between the contact surface and the tire keeps the tirefrom slipping (relative to the contact surface) and allows power to betransferred from the motor to the wheel. The force of friction equalsthe normal force (of the contact surface against the tire) times thecoefficient of friction, which may be expressed as follows:

F _(f) =μ*F _(N)

where F_(f) is the force of friction, μ is the coefficient of friction,and F_(N) is the normal force between the contact surface and the tire.The coefficient of friction is subject to change based on conditionslike the weather. For example, when it rains and the tire becomes wet,the coefficient of friction typically drops significantly, reducing theforce of friction for a given normal force. As another example, thecoefficient of friction may be reduced if the tire becomes dusty ormuddy.

When the coefficient of friction is suddenly reduced—for example, whenthe tire becomes wet after going through a puddle—slippage can occurbetween the tire and the contact surface. Such slippage can bedangerous, because it can result in sudden and unpredictable changes tothe power delivered to the wheel. For example, after slipping, the tiremay suddenly reengage (or “catch”) with the contact surface, causing asudden increase in the power delivered to the wheel and in the resultingspeed of the vehicle.

Known friction drive systems have difficulty responding to rapid changesin the amount of friction caused by weather (e.g., rain or snow), roadconditions (e.g., dust or dirt), and other factors (e.g., loss of air inthe tire). Some known systems use contact surfaces, such as sandpaper,having a high coefficient of friction to reduce slippage during changingconditions. However, such high-friction surfaces dramatically increasetire wear. Moreover, the sandpaper (or other high-friction surface)needs to be regularly replaced as it wears down, which is a tedious andtime consuming process that requires regular monitoring by the consumer.

Another way to protect a friction drive system against changes infriction (e.g., due to changing road conditions) is to adjust the normalforce between the contact surface and the tire. For example, a frictiondrive system could be configured to always provide a large normal forcebetween the contact surface and the tire. However, continuouslymaintaining a large normal force requires more power due to tirechurning, which drains the battery, and also increases tire wear.

In most known systems, the position of the contact surface relative tothe tire is fixed when the friction drive system is installed. Thisfixed position, in turn, determines the normal force. In other systems,the normal force is set by a spring mechanism, gravity, or other biasingforce. Still other systems provide a limited ability to adjust thenormal force by manually reconfiguring the system, for example, bypulling a lever, however, such systems are difficult to control andtypically require the user to stop the vehicle and dismount in order tochange the settings.

None of these known friction drive systems provide a simple mechanismfor adjusting the normal force. None of these known friction drivesystems adjust the normal force dynamically in response to changing roadconditions, weather, and the like. None of these known friction drivesystems provide automatic traction control between the friction driveand the tire (or wheel). None of these known systems optimize the normalforce to provide sufficient friction to avoid slippage while minimizingtire wear and maximizing battery efficiency.

Another problem with known friction drive systems is that they do notautomatically disengage from the tire (or wheel) when the motor is nolonger in use. Engaging with the tire (or wheel) when the motor is notactively providing power causes drag on the system, reduces efficiency,and slows the vehicle. Some known systems permit the user to manuallydisengage the motor by means of a lever or similar mechanism, whichmoves the contact surface away from the tire. However, such systems areinefficient because the user frequently forgets to disengage the contactsurface or is unable to disengage (and reengage) the contact surfacewith optimal timing. Such known systems can also be dangerous; if theuser reengages the contact surface when it is spinning at ahigh-differential speed compared to the wheel, the power delivered tothe wheel (and the resulting speed of the vehicle) may change suddenlyand unpredictably.

Accordingly, there is a need in the art for friction drive systems—andcontrol algorithms for such systems—that can better adjust to changes infriction caused by road conditions, weather, and the like. There is aneed in the art for an automatic traction control system for a frictiondrive that avoids slippage while minimizing tire wear and maximizingbattery efficiency. There is also a need in the art for a system andmethod of automatically disengaging and reengaging the contact surfaceof a friction drive with the tire (or wheel) of a wheeled vehicle in asafe and efficient manner.

SUMMARY OF THE DISCLOSURE

The present disclosure includes improved friction drive systems, controlalgorithms for friction drive systems, and automatic traction controlfor friction drive systems. Embodiments of the present disclosure mayimprove control over an amount of normal force between a contact surfaceon a friction drive (e.g., disposed on a drive motor) and a tire orwheel of a wheeled vehicle. Embodiments of the present disclosure mayinclude an automatic traction control system for a friction drive thatautomatically adjusts the normal force to avoid slippage whileminimizing tire wear and maximizing battery efficiency. Embodiments ofthe present disclosure may dynamically adjust the normal force betweenthe contact surface and the tire (or wheel) in response to rapidlychanging conditions, such as weather, road surface, and/or tireinflation. Embodiments of the present disclosure may allow a user tocalibrate or adjust the amount of normal force delivered based on theirpreferences or based on a selected mode of operation. Embodiments of thepresent disclosure may automatically disengage and reengage the contactsurface of a friction drive with the tire (or wheel) of a wheeledvehicle in a safe and efficient manner.

Embodiments of the present disclosure may include an initializationprocedure for determining a starting position of the contact surfacerelative to the tire, which advantageously may allow for rapidengagement with the tire when power is needed. Embodiments of thepresent disclosure may include a procedure for automatically engagingand disengaging the contact surface with the tire, such that engagementoccurs when the motor is delivering power. Embodiments of the presentdisclosure may deliver power to the drive motor in response to athrottle mechanism. Embodiments of the present disclosure may include aTailwind operating mode that simulates the effect of a tailwind byproviding a constant level of power to the drive motor. Embodiments ofthe present disclosure may deliver power to the drive motor in responseto a Pedal Assist Sensor.

As would be understood by a person of skill in the art, embodiments ofthe present disclosure have applications beyond wheeled vehicles and maybe used to improve the function, control, and performance of frictiondrive systems generally.

The present disclosure includes embodiments of a friction drive systemhaving a drive assembly, a control unit, and a battery unit. The driveassembly may include a motor and a contact surface capable of engagingwith a tire of a wheeled vehicle. The control unit may include anautomatic traction control system capable of automatically adjusting anamount of friction between the contact surface and the tire when thefriction drive system is mounted to the wheeled vehicle. The controlunit may determine an amount of electrical current to deliver from thebattery unit to the motor based at least in part on an input signal.

The present disclosure includes embodiments of a friction drive systemhaving a drive assembly including a motor and a pivot mechanism. Acontact surface may be disposed on the motor, and the motor may beattached to an end of the pivot mechanism. An automatic traction controlsystem may be capable of automatically adjusting an angle of the pivotmechanism in response to one or more sensed conditions.

The present disclosure includes embodiments of a method for automatictraction control of a friction drive system in which a pivot mechanismmay be rotated by powering a gear motor until a current drawn by thegear motor exceeds a threshold value. A first speed of a drive motorconnected to the pivot mechanism may be detected when the drive motor isunpowered. Power may be applied to the drive motor such that a secondspeed of the drive motor matches the detected first speed of theunpowered drive motor. Power to the drive motor may be increased untilthe drive motor reaches a third speed determined at least in part froman input signal. Power to the drive motor may be cut when a rate ofchange of drive motor speed exceeds a threshold value.

The present disclosure includes embodiments of a friction drive systemhaving a battery unit capable of delivering power to a drive assembly.The drive assembly may include a motor and a contact surface and have ameans for automatically controlling an amount of normal force deliveredby the contact surface in response to one or more sensed conditions. Thedrive assembly may also include a pivot mechanism and the contactsurface may be disposed on a rotating mechanism attached to the pivotmechanism (e.g., a drive motor or roller).

The present disclosure includes embodiments of a method for automatictraction control of a friction drive system in which a pivot mechanismmay be rotated with a gear motor until a current drawn by the gear motorexceeds a threshold value. A first speed of a drive motor connected tothe pivot mechanism may be detected when the drive motor is unpowered.Power may be applied to the drive motor such that a second speed of thedrive motor matches the detected first speed of the unpowered drivemotor. Power to the drive motor may be increased until the drive motorreaches a third speed determined at least in part from an input signal.Power to the drive motor may be reduced (including up to cutting thepower completely) when a rate of change of drive motor speed exceeds athreshold value. After reducing power to the drive motor, the pivotmechanism may be rotated such that the current drawn by the gear motorincreases.

The foregoing discussion in the Summary of the Disclosure is for exampleonly and is not intended to limit the scope of the claimed invention(s)or the embodiments described below

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram showing an embodiment of a friction drivesystem with a battery unit, control unit, and drive assembly.

FIG. 1B is a block diagram showing another embodiment of a frictiondrive system with a battery unit, control unit, and drive assembly.

FIG. 1C shows an embodiment of a throttle mechanism that may provide aninput signal to the control unit.

FIG. 2A shows an embodiment of a unitary friction drive system having apivoting mechanism in an expanded position.

FIG. 2B shows an embodiment of a unitary friction drive system having apivoting mechanism in a retracted position.

FIG. 2C shows an embodiment of a unitary friction drive system prior tobeing mounted on a bicycle having a mount.

FIG. 2D shows a closer perspective of an embodiment of a unitaryfriction drive system prior to being mounted on a mount.

FIG. 2E shows an embodiment of a unitary friction drive system mountedon a bicycle with a pivoting mechanism in an engaged position.

FIG. 2F shows a cut-away view of an embodiment of a unitary frictiondrive system mounted on a bicycle with a pivoting mechanism in anengaged position.

FIG. 3A shows an embodiment of a friction drive system having twobattery packs attached to a case.

FIG. 3B shows an embodiment of a friction drive system having twobattery packs detached from a case.

FIG. 4A shows an example of a three-unit embodiment of a friction drivesystem in which a control unit, a battery unit, and a drive assembly areattached together and mounted adjacent to a front wheel of a wheeledvehicle.

FIG. 4B shows an example of a three-unit embodiment of a friction drivesystem in which a control unit and a drive assembly are attachedtogether and mounted adjacent to a front wheel of a wheeled vehicle; anda battery pack is mounted to a frame of the wheeled vehicle.

FIG. 4C shows an example of a three-unit embodiment of a friction drivesystem in which a control unit, a battery unit, and a drive assembly aremounted adjacent to a rear wheel of a wheeled vehicle

FIG. 4D shows an example of a three-unit embodiment of a friction drivesystem in which a control unit and a drive assembly are attachedtogether and mounted adjacent to a rear wheel of a wheeled vehicle, anda battery pack is mounted to a frame of the wheeled vehicle.

FIG. 4E shows an example of a three-unit embodiment of a friction drivesystem in which a drive assembly is mounted adjacent to a front wheel ofa wheeled vehicle; and a battery pack and a control unit are attachedtogether and mounted to a frame of the wheeled vehicle.

FIG. 4F shows an example of a control unit coupled to a drive assembly,where the drive assembly includes a motor mount assembly capable ofcoupling with a mount.

FIG. 5A shows an embodiment of a friction drive system wherein a controlunit and a drive assembly are mounted to a mount adjacent to a frontwheel of a wheeled vehicle such that a contact surface is engaged withthe tire; and the drive assembly is capable of pivoting relative to themount.

FIG. 5B shows a close-up of the boxed region in FIG. 5A.

FIG. 6 shows an embodiment of a drive assembly where an angle of apivoting mechanism initially is set to a disengaged position relative toa tire, but the pivoting mechanism may swing into an engaged positionusing motor torque or by a secondary motorized pivot control mechanism.

FIG. 7 shows an embodiment of a drive assembly with a pivoting mechanismthat has a freedom of angular motion about an initial angle which may becontrolled.

FIG. 8A shows a front view of an embodiment of a drive assembly havingadjustable knobs for controlling a range of angular motion of a pivotingmechanism.

FIG. 8B shows a side view of an embodiment of a drive assembly havingadjustable knobs for controlling a range of angular motion of a pivotingmechanism.

FIG. 9 shows an embodiment of a drive assembly having a worm gear forcontrolling an angle of a pivot bracket on the drive assembly and, thus,an amount of normal force between a contact surface on the driveassembly and a tire.

FIG. 10A shows an example of a flow chart for a start-up/initializationprocess for embodiments of a friction drive system

FIG. 10B shows another example of a flow chart for astart-up/initialization process for embodiments of a friction drivesystem.

FIG. 11 shows an example of a flow chart for a shut-down/reset procedurefor embodiments of a friction drive system

FIG. 12A shows an example of a flow chart for a start-up/initializationprocess for embodiments of a friction drive system when in a Tailwindmode.

FIG. 12B shows another example of a flow chart for astart-up/initialization process for embodiments of a friction drivesystem when in a Tailwind mode.

FIG. 13 shows an example of a flow chart for responding to depressionand release of a throttle in embodiments of a friction drive system.

FIG. 14 shows an example of a flow chart for engaging a drive motor inembodiments of a friction drive system.

FIG. 15 shows an example of a flow chart for disengaging a drive motorin embodiments of a friction drive system

FIG. 16 shows an example of a flow chart for automatically detecting andcorrecting slippage that may be used in embodiments of friction drivesystem.

FIG. 17 shows another example of a flow chart for automaticallydetecting and correcting slippage that may be used in embodiments offriction drive system.

FIG. 18 shows yet another example of a flow chart for automaticallydetecting and correcting slippage that may be used in embodiments offriction drive system.

DETAILED DESCRIPTION

As shown in FIG. 1A, in embodiments of the disclosure, friction drivesystem 100 may include control unit 101, battery unit 102, and driveassembly 103. Battery unit 102 may provide electrical power to controlunit 101 and/or to drive assembly 103. Control unit 101 may providecontrol information and/or commands to battery unit 102 and/or driveassembly 103. Drive assembly 103 may provide power to a tire or wheel ofa wheeled vehicle, or it may provide power to a hub or crank assembly,or it may provide power to and/or portion of the wheeled vehicle. Invarious embodiments of the disclosure, control unit 101, battery unit102, and drive assembly 103 may be provided as separate connecting unitsor as a single integrated unit. Friction drive system 100 also may beintegrated with a wheeled vehicle, for example, as an electric bicycleor scooter.

As shown in the embodiment of FIG. 1B, drive assembly 103 may includemotor 104 and, optionally, one or more rollers (not shown). Driveassembly 103 may be capable of engaging with tire 202 (or directly withwheel 201), such that motor 104 delivers mechanical power to wheel 201.For example, drive assembly 103 may engage with tire 202 via a contactsurface disposed on the outer surface of motor 104 and/or on one or morerollers. Control unit 101 may interact with battery unit 102 to controlthe amount of electrical power delivered to drive assembly 103 (andmotor 104), thereby controlling the amount of mechanical power deliveredto wheel 201. In embodiments of the disclosure, wheel 201 may be a frontor a rear wheel of a bicycle, for example.

As shown in FIG. 1B, control unit 101 may include brushless DC motorcontroller (“BLDC”) 106. BLDC 106 may regulate the delivery ofelectrical current (and/or power) from battery unit 102 to driveassembly 103. For example, electrical current may flow from battery unit102 to BLDC 106 and then to drive assembly 103 via power lines 131 and111. BLDC 106 may regulate the amount of current (and/or power)delivered to drive assembly 103 in response to commands from controlunit 101. In some embodiments, power line 111 may include at least threehigh-power signals for delivering electrical current to motor 104. Othersignals also may be provided in power line 111, such as signals fordelivering information about the sensed position of motor 104 to BLDC106, as would be understood by a person of skill in the art in view ofthe present disclosure. In other embodiments, not shown, drive assembly103 may include BLDC 106 and/or additional components (e.g., hardware,firmware, circuitry) for controlling electrical current delivered tomotor 104

As would be understood by a person of skill in the art in view of thepresent disclosure, the physical relationships between electricalcurrent, voltage, and power are well-known and these values can becalculated from one another, given other known parameters of the system(e.g., electrical resistance). In addition, for any given motor, motortorque may be calculated from motor current. Thus, control decisions maybe based on electrical current, power, voltage, and/or motor torque (inaddition to other parameters). In embodiments of the disclosure, acontrol algorithm running on a processor in control unit 101 maydetermine a desired electrical current to supply from BLDC 106 to motor104.

As shown in FIG. 1B, control unit 101 may receive input signal 110.Input signal 110 may be generated in response to a user input. Inputsignal 110 may be delivered over a physical cable or wirelessly usingBluetooth, IEEE 802.11, or other suitable wireless technology. Forexample, input signal 110 may be generated by a throttle mechanism (suchas the throttle 115 in FIG. 1C) operated by a user, and input signal 110may contain information representing the amount of activation of thethrottle mechanism (e.g., in the form of an analog or digital signal).Control unit 101 may then use input signal 110 to determine how muchelectrical current (and/or power) should be delivered to drive assembly103, for example, by increasing the amount of current as the throttle isactivated further (e.g., as the user presses the throttle inward). Insome embodiments, feedback signal 112 may provide control unit 101 withinformation from drive assembly 103, including information about motor104, such as motor RPM, motor current draw, motor phase position, and/ormotor temperature. Feedback signal 112 also may include otherinformation, such as power and torque information, as well as measuredproperties of wheel 201 and/or tire 202 (e.g., wheel speed,acceleration, surface properties) and other sensed information. Feedbackline 112 may be provided separately or together with power line 111.Alternatively, feedback may be provided wirelessly using Bluetooth, IEEE802.11, or other suitable wireless technology. As discussed furtherbelow, control unit 101 also may include Automatic Traction ControlSystem (“ATCS”) 150 for automatically adjusting an amount of frictionbetween motor 104 and tire 202.

Control unit 101 and ATCS 150 may include memory for storinginformation, such as information about the state of friction drivesystem 100 and/or wheeled vehicle 200. As used herein, “memory” mayinclude RAM, ROM, buffers, registers, or other electronic means ofstoring information, as would be understood by one of skill in the artin view of the present disclosure.

FIG. 1C shows an example of a throttle mechanism, throttle 115, that maygenerate input signal 110 delivered to control unit 101. Throttle 115may include plunger 116, which may be depressed by a user's thumb when auser desires to power motor 104. Plunger 116 may include a linearposition sensor that generates a signal correlated to the position ofplunger 116. Alternatively, or in addition, throttle 115 may have athrottle button with a pressure sensor or force sensing resistor thatgenerates a signal correlated to how hard a user presses on the button.In other embodiments, a twist throttle may be used.

In other embodiments of the disclosure, input signal 110 may begenerated by a Pedal Assist Sensor (“PAS,” not shown), and input signal110 may contain information representing the torque delivered to thepedals, the speed of pedal rotation, the power delivered to the pedals,and/or other measurable properties of the pedals. Control unit 101 maythen use information in input signal 110 to determine how much current(and/or power) to deliver to drive assembly 103, for example, byincreasing the amount of current as the pedal torque increases (e.g., asthe user presses down harder on the pedals).

In yet other embodiments of the disclosure, input signal 110 may includeinformation generated by both a throttle mechanism and a PAS, and thisinformation may be used together to control the delivery of electricalpower to drive assembly 103. For example, the PAS may be used todetermine the base level of electrical power, while the throttlemechanism may allow the user to provide extra power from the motor asdesired.

In still other embodiments of the disclosure, input signal 110 may begenerated by sensors—such as a vehicle speed sensor, accelerometer, ormotor current sensor—without requiring user input. For example, inputsignal 110 may contain information indicating vehicle speed oracceleration, and control unit 101 may use this information to determinehow much electrical current to deliver to drive assembly 103. In stillfurther embodiments, input signal 110 may contain information generatedby sensors attached to the user—such as a heart rate monitor, bloodpressure monitor, fitness tracker, or other wearable device—and thisinformation may be used to determine how much electrical current todeliver to drive assembly 103. For example, control unit 110 may varythe electrical current delivered to drive assembly 103 in order tomaintain the user's heart rate within a certain range by decreasingcurrent when the heart rate goes below the target range (requiring theuser to pedal harder) and increasing current above the target range(making it easier to pedal). As would be apparent to one of skill in theart in view of the present disclosure, input signal 110 may includevarious information—provided as one or multiple signals in analog ordigital form—which may be used together to make control decisionsregarding how much electrical current (and/or power) to deliver to driveassembly 103 (and/or motor 104).

Control unit 101 may use other information—in addition to or instead ofinput signal 110—in determining how much electrical current to deliverto drive assembly 103. This other information may be measured directlyby sensors or may be derived from known physical relationships (e.g.,between mechanical power, torque, and speed). For example, control unit101 may take into account vehicle speed, vehicle acceleration, wheeltorque, wheel speed (or RPM), pedal torque, pedal speed, pedal power,motor torque, motor speed (or RPM), motor power, motor current, motortemperature, battery voltage, battery power, battery temperature, andother related factors when determining how much electrical power todeliver to drive assembly 103.

As used herein, the term “motor speed” refers to any quantifiablemeasurement of the speed of a motor, including RPM and tangential speed.Similarly, the term “wheel speed” refers to any quantifiable measurementof the speed of a wheel, including RPM and tangential speed. It ispossible to calculate tangential speed from RPM—and vice-a-versa—giventhe diameter of the circular body. In embodiments of the disclosure,wheel speed may be determined from motor speed, because the tangentialspeed of contact surface 109 should equal the tangential speed of tire202 when the surfaces are engaged without slippage. Furthermore, inembodiments of the disclosure, motor RPM may be used as a proxy forwheel RPM, because the two values normally will be related by a fixedconstant.

Embodiments of friction drive system 100 are designed to be portable andeasily attachable and removable from a wheeled vehicle. As shown in theexemplary embodiments of FIGS. 2A to 4C, friction drive system 100 maybe provided as a single unit, as a unit with detachable components, asmultiple separate units with connectable parts, or as stand-alone units.

FIGS. 2A to 2F show an embodiment of friction drive system 100 in whichcontrol unit 101, battery unit 102, and drive assembly 103 are disposedas a single unit inside case 120. In some embodiments, case 120 may becomposed of plastic, metal, ceramic, or other suitable materials;alternatively, case 120 may include multiple pieces attached together.Case 120 also may include handle 124 for easily carrying friction drivesystem 100 when it is not attached to a wheeled vehicle.

As shown in FIG. 2A, drive assembly 103 may include pivot arm 107, whichmay allow motor 104 (and/or rollers 105, not shown) to rotate into aposition of contact with a tire of a wheeled vehicle, when frictiondrive system 100 is mounted to the wheeled vehicle. For example, motor104 may attach to pivot arm 107, and pivot arm 107 may be adjustablebetween a retracted position and an expanded position. FIG. 2A showspivot arm 107 in an expanded position with contact surface 109 of motor104 exposed and capable of engaging with a tire (e.g., when mounted).

FIG. 2B shows pivot arm 107 in a retracted position with motor 104partially enclosed within a recess in case 120. Placing pivot arm 107 inthe retracted position may protect the motor from damage, protect theuser from inadvertent activation of the motor, and/or protect the userfrom dirt and/or grime on contact surface 109. Friction drive system 100also may be more streamlined and easier to carry when pivot arm 107 isin the retracted position.

As shown in FIGS. 2C to 2F, friction drive system 100 also may includemounting mechanism 121 for rapid attachment and removal to/from mount210 disposed on a wheeled vehicle (e.g., a bicycle). As shown in FIG.2C, mount 210 on the wheeled vehicle may have a triangular shape. Forexample, some bike share bicycles have a triangle bracket on the frontof the bicycle for interfacing with a docking station; this triangularbracket may serve as mount 210 in embodiments of the disclosure. Asanother example, a bicycle owner may install a triangular mount on theirbicycle for the purpose of mounting friction drive system 100.

As shown in FIG. 2D, mounting mechanism 121 may include triangularreceptacle 122, which may be formed integral with case 120. The arrow inFIGS. 2C and 2D indicates the direction of motion of case 120 relativeto mount 210 when coupling receptacle 122 to mount 210. FIG. 2E showscase 120 coupled to mount 210, such that drive assembly 103 contactstire 202 when pivot arm 107 is in the expanded position. FIG. 2F is acut-away view of drive assembly 103 showing sliding plunger mechanism123 for securely coupling friction drive system 100 to mount 210. Forexample, sliding plunger mechanism 123 may be spring-loaded and may havea protrusion that slides into a corresponding opening on mount 210.

In view of the present disclosure, a person of skill in the art wouldunderstand that mounting mechanism 121 may be configured to couple withvarious types of mounts, for example, by changing the shape oftriangular receptacle 122 and/or the location of sliding plungermechanism 123 (or other fastening mechanism). Moreover, in embodimentsof the disclosure, triangular receptacle 122 may be disposed on otherportions of case 120 or separately on battery unit 102 and/or driveassembly 103.

FIGS. 3A and 3B show an embodiment of friction drive system 100 wherebattery unit 102 includes two battery packs 108 designed for quickattachment and release from case 120 using quick release mechanism 125.FIG. 3A shows battery packs 108 attached to case 120, and FIG. 3B showsbattery packs 108 detached from case 120. In the embodiment of FIGS. 3Aand 3B, battery packs 108 may be easily swapped out for fresh batterieswhen the charge becomes depleted. Moreover, the use of dual batterypacks 108 may provide a larger total battery capacity for the system,increasing range. In addition, this embodiment allows for the use ofdifferent size batteries in different situations. For example, whentraveling, individual battery packs 108 may be sized to comply with airtravel restrictions on Lithium-battery sizes; larger battery packs 108may be used when at home. Other features of the embodiment of FIGS. 3Aand 3B may be similar to those described with respect to the embodimentof FIGS. 2A-F.

FIGS. 4A to 4F show embodiments of friction drive system 100 wherecontrol unit 101, battery unit 102, and drive assembly 103 are providedin three separate units, which may be attached to one another in variousconfigurations. The three units may be capable of connecting together inany or all of the configuration shown in FIGS. 4A to 4F (and otherconfigurations, not shown), depending on the particular vehicle and thedesire of the user. Although FIGS. 4A to 4E depict a bicycle, otherwheeled vehicles also may be used.

FIG. 4A shows a three-unit embodiment of friction drive system 100 inwhich control unit 101, battery unit 102, and drive assembly 103 areprovided in three separate units; however, in this configuration, allthree units attach together and mount to wheeled vehicle 200 adjacent towheel 201. In the example of FIG. 4A, drive assembly 103 is shownmounted above the front wheel of a bicycle, such that drive assembly 103may engage with tire 202 (e.g., via contact surface 109 on motor 104).As shown in FIG. 4A, drive assembly 103 may include motor mount assembly140 for attaching to mount 210 on wheeled vehicle 200. Alternatively, amounting mechanism may be disposed on control unit 101 and/or batteryunit 102.

FIG. 4B shows a configuration of a three-unit embodiment of frictiondrive system 100 in which second mounting mechanism 130 may be disposedon battery unit 102 for coupling with second mount 211 on wheeledvehicle 200. In this embodiment, control unit 101 and drive assembly 103may be attached together and independently mounted via mount 121. Line131 may provide power (e.g., as a two-conductor DC signal) from batteryunit 102 to control unit 101 (or directly to drive assembly 103). Line131 may be detachable (e.g., via barrel, coaxial, USB or otherelectrical connection) from battery unit 102 and/or control unit 101.Battery unit 102 also may exchange information with control unit 101 viasignals transmitted over line 131, such as information about batterystate provided by a Battery Management System (“BMS”). Alternatively,battery state information may be provided wirelessly using Bluetooth,IEEE 802.11, or other suitable wireless technology.

The embodiment of FIG. 4B may provide the advantage of mounting batteryunit 102 separately to the frame of the bicycle, thereby reducing theweight of the portion of friction drive system 100 that is disposedadjacent to the wheel (e.g., above the wheel in some embodiments).Reducing the weight mounted adjacent to the wheel may, for example,provide for smoother steering and enhanced stability. In addition,mounting battery unit 102 separately on the body of wheeled vehicle 200may reduce strain on mounting mechanism 121 and reduce the impact of anyvibrations. In still other embodiments of the disclosure (as shown inFIG. 4E), control unit 101 may be mounted together with battery unit 102on the body of wheeled vehicle 200, further reducing the weight of thesystem mounted adjacent to the wheel.

FIG. 4C shows yet another configuration of a three-unit embodiment offriction drive system 100 in which control unit 101, battery unit 102,and drive assembly 103 may be attached together and mounted to the frameof a bicycle (or other wheeled vehicle); however, unlike in FIG. 4A, inthis embodiment the three units are connected together and mountedadjacent to a rear wheel of wheeled vehicle 200, depicted as a bicyclein this example.

FIG. 4D shows still another configuration of a three-unit embodiment offriction drive system 100 in which control unit 101 and drive assembly103 may be attached together and mounted above a rear wheel of wheeledvehicle 200. As shown in FIG. 4D, battery unit 102 may be mountedseparately onto the frame of wheeled vehicle 200. As described inreference to FIG. 4B, line 131 may provide power (e.g., as a DC signal)from battery unit 102 to control unit 101 (or directly to drive assembly103).

FIG. 4E shows a further configuration of a three-unit embodiment offriction drive system 100 in which drive assembly 103 may be mounted byitself above a front wheel of wheeled vehicle 200. As show in FIG. 4E,battery unit 102 and control unit 101 may be attached together andmounted to the frame of the bicycle. In this embodiment, line 131 maycarry a three phase power signal from BLDC 106, and line 131 also maycarry one or more signals for controlling drive assembly 103.

A person of skill in the art, in view of the present disclosure, wouldunderstand that drive assembly 103 could also be mounted by itself abovea rear wheel of wheeled vehicle 200; furthermore, drive assembly 103could be modified (or replaced) to act as a hub motor, mid-drive, orother motorized system for delivering power to a wheeled vehicle

In FIGS. 4A to 4E, drive assembly 103 may include motor mount assembly140 for attaching to mount 210 in a position adjacent to the front orrear wheel of the bicycle (or other wheeled vehicle). In someembodiments, motor mount assembly 140 may include triangular receptacle122 and sliding plunger mechanism 123 for coupling with a bike sharebicycle; alternatively, motor mount assembly 140 may be adapted tocouple with other types of mounts and/or vehicles. Notably, the threeunits of friction drive system 100 may be designed such that they can beattached in any of the configurations of FIGS. 4A to 4D, as desired bythe end-user, and/or in other configurations not shown.

FIG. 4F shows an example of motor mount assembly 140 which is capable ofcoupling with mount 210. As shown in FIG. 4F, control unit 101 mayattach to drive assembly 103, which may include motor mount assembly140. Motor mount assembly 140 may include a groove and dual-pistons 126for securely coupling with mount 210; alternatively, one or more slidingplunger mechanisms (or other coupling mechanisms) may be used instead ofdual-pistons 126. Mount 210 may, for example, be attached to wheeledvehicle 200 adjacent to a front or rear wheel, such that drive assembly103 may deliver power to the wheel when securely coupled to mount 210.

Embodiments of friction drive system 100 having a three-unit design, asexemplified in FIGS. 4A-F, may be highly configurable and adaptable todifferent vehicles, which may have different mounting requirements. Thethree-unit design may provide greater flexibility and may significantlyreduce costs to the user, as compared to other designs, becausedifferent units may be used interchangeably depending on the vehicletype and desired setup. For example, battery unit 102 may easily bereplaced with a fresh battery when the charge runs low or upgraded toprovide more capacity, power, etc., without replacing the other units.As another example, different sized batteries may be used with differentvehicles (e.g., a smaller battery with a scooter as compared to abicycle) without replacing the other units. As yet another example, thesame battery unit 102 and control unit 101 may be used with differentdrive assemblies 103 designed for use with different types of vehiclesand/or designed to power a vehicle in different manners. For example,some drive assemblies may be designed to power a bicycle, while othersmay be designed to power a scooter; some drive assemblies may power thefront wheel, others may power the rear wheel, still others may power thehub of the front or rear wheel, and yet others may power the crank orpedal assembly. The three-unit design makes it possible to use the samebattery and controller with various custom drive assemblies. In asimilar manner, different control units 101 may be used with the samebattery unit 102 and/or drive assembly 103. Thus, embodiments of thedisclosure having a three-unit design may provide a great deal offlexibility to the manufacturer, retailer, and end user by allowingcomponents to be used interchangeably.

FIGS. 5A and 5B show an embodiment of friction drive system 100 whereincontrol unit 101 and drive assembly 103 are mounted to mount 210 onwheeled vehicle 200. FIG. 5B shows a close-up view of the boxed regionin FIG. 5A. As shown in FIGS. SA and SB, in embodiments of thedisclosure the amount of normal force between contact surface 109 andtire 202 may be determined, at least in part, by distance d whichcontact surface 109 presses into tire 202. An angle θ may be defined asthe angle between the center of wheel 201 and pivot point P1 of driveassembly 103 relative to the line from P1 through the center of drivemotor 104. Decreasing angle θ towards 0 degrees increases distance d andthe amount of normal force, F_(N). As previously explained, the amountof friction is proportional to the normal force (for a given coefficientof friction, μ). Therefore, in some embodiments, the amount of frictionmay be controlled through angle θ. The distance between P1 and P2, whereP2 is the intersection of the outer edge of contact surface 109 with theline from P1 through the center of drive motor 104, determines how muchangle θ must vary to increase distance d by a given amount at a givenposition of angle θ. As one of skill in the art would understand in viewof the present disclosure, the amount of change in distance d (and thusthe normal force) for a given change in angle θ may be controlled bychanging the relative proportions of the friction drive system, as amatter of design choice.

In view of the present disclosure, one of skill in the art wouldunderstand that in other embodiments of the disclosure, depending ondesign choice and how angle θ is defined, increasing angle θ mayincrease distance d and the normal force and, conversely, decreasingangle θ may decrease distance d and the normal force.

In some embodiments, contact surface 109 of drive assembly 103 mayalways be engaged with tire 202. In alternative embodiments, asillustrated in FIG. 6, contact surface 109 may engage and disengage withtire 202 on-demand. As shown in FIG. 6, starting value θ₁ of angle θ maybe set such that contact surface 109 is disengaged from tire 102 whenmotor 104 is not running. When powered, motor 104 generates torque thatmay pull pivot arm 107 into tire 202. A biasing force (e.g., from aspring mechanism, not shown) may return pivot arm 107 to its startingposition when motor 104 is unpowered. Thus, embodiments of thedisclosure may automatically engage and/or disengage contact surface 109with tire 202 using torque from motor 104, thereby eliminating drag onthe system and preventing wear when motor 104 is not in use.

FIG. 7 shows an embodiment where starting value θ₁ is set to engagecontact surface 109 with tire 202 and to provide enough friction topower wheel 201 during normal conditions (e.g., not raining, drypavement, etc.). Value θ₁ may be preset, determined through calibration,set when mount 210 is installed, and/or set when drive assembly 103 iscoupled to mount 210. In the embodiment of FIG. 7, angle θ may varyabout θ₁ by a predetermined amount, which may be from 3° to 5° in someembodiments. As shown in FIG. 7, when angle θ is decreased by apredetermined amount from θ₁ (indicated by the “−” sign) the normalforce and the amount of friction may increase, thereby preventingslippage between contact surface 109 and tire 202 in wet or slipperyconditions, for example. On the other hand, when angle θ is increased bya predetermined amount (indicated by the “+” sign), contact surface 109may completely lose contact with tire 102. For example, it may bedesirable to disengage contact surface 109 from tire 202 when motor 104is not providing power in order to prevent drag on wheel 201, whichcould slow vehicle 200. Disengaging contact surface 109 from tire 202also may prevent wear to tire 202 and motor drive assembly 103.

In embodiments of the disclosure, angle θ may vary freely within alimited range about initial value θ₁. The value of θ₁ itself may bevaried in a controlled manner—either manually or automatically—dependingon road conditions, weather, and the like. When angle θ is free to varywithin a few degrees about θ₁, torque from motor 104 may act toautomatically adjust the amount of friction as needed. For example, whentorque from motor 104 increases in response to a user pressing thethrottle, this may cause a pivoting mechanism to swing downwards,pressing contact surface 109 into tire 202 and increasing the amount offriction. Conversely, when torque from motor 104 decreases, rotation ofthe wheel may push contact surface 109 away from tire 202, therebyreducing the amount of friction. Advantageously, this automaticadjustment in friction may occur without the need for intervention bythe user and without requiring a specific control algorithm.Nonetheless, it may still be desirable to change the value of θ₁ in acontrolled manner depending on road conditions, weather, and the like,because the freedom of motion about θ₁ may provide only a limited amountof automatic adjustment.

In embodiments of the disclosure, angle θ may be allowed to vary freelywithin about plus or minus 3° of θ, and the value of θ₁ may itself beadjustable within about plus or minus 15°. Allowing θ₁ to be adjustedmay provide greater ability to customize the configuration for aparticular wheeled vehicle or for particular road and/or weatherconditions. In other embodiments of the disclosure, angle θ may not beallowed to vary freely and may be constrained to the value of 01.Nonetheless, the value of θ₁ itself may still be varied in a controlledmanner, either manually or automatically. Constraining the value ofangle θ to equal θ₁ may provide more precise control over the amount offriction in some embodiments of the disclosure. For example, in someembodiments, Automatic Traction Control System 150 may determine theprecise value of angle θ₁ for optimal performance.

FIGS. 8A and 8B show an embodiment of friction drive system 100 having aunitary design, wherein the allowed variation of angle θ may becontrolled by adjustment knobs 160 and 161. As illustrated in FIG. 8A,adjustment knob 160 maybe used to control the maximum value of angle θ,thereby limiting the minimum amount of friction between contact surface109 and tire 202. Turning adjustment knob 160 in the direction of arrow301 may pivot motor assembly 103 inward toward tire 202 and/or preventangle θ from exceeding a certain value, thereby increasing the minimumamount of friction that may be provided (e.g., a smaller angle θcorresponds to a greater amount of friction in this embodiment).Similarly, as illustrated in FIG. 8B, adjustment knob 161 may be used tocontrol the minimum value of angle θ, thereby limiting the maximumamount of friction between contact surface 109 and tire 202. Turningadjustment knob 161 in the direction of arrow 303 may pivot motorassembly 103 outward away from the tire and/or prevent angle θ fromdecreasing below a certain value, thereby reducing the maximum amount offriction that may be provided.

Knobs 160 and 161 may have various settings (e.g., five settings in FIG.8A) which may physically limit the range of motion of pivot arm 107,thereby constraining angle θ. Knobs 160 and 161 may be adjusted manuallyby a user, or automatically by stepper motors or the like (not shown)controlled by control unit 101. One of skill in the art, in view of thepresent disclosure, would understand that knobs 160 and 161 also be usedwith other embodiments and configurations of friction drive system 100including with a three-unit embodiment as illustrated in FIGS. 4A-F.

FIG. 9 shows an embodiment of drive assembly 103 having motor mountassembly 140 and pivot bracket 141. In this embodiment, pivot bracket141 may have a pre-set pivot range of about 30° (plus or minus 15° abouta starting position) relative to motor mount assembly 140. As shown inFIG. 9, pivot bracket 141 may have a rounded circumference with teethcapable of engaging with worm gear 142. Worm gear 142 may be anchored tomotor mount assembly 140 and control the value of angle θ₁ (and/or arange of values of angle θ about θ₁) between pivot bracket 141 and motormount assembly 140. For example, turning worm gear 142 may rotate pivotbracket 141 relative to motor assembly 140, thereby changing angle θ₁and the resulting normal force between contact surface 109 and tire 202.Worm gear 142 may be rotated manually via knob 144 and/or automaticallywith gear motor 145. In some embodiments, gear motor 145 may be astepper motor, a standard DC motor, or other motor capable ofcontrolling worm gear 142. In some embodiments, both knob 144 for manualadjustment and gear motor 145 for automatic adjustment may be provided,thereby allowing a user to manually calibrate the system through knob144 while also benefiting from automatic control during normal use.Furthermore, rather than knob 144, another control may be used to allowthe user to manually adjust the normal force; for example, a slider ordial may be provided on friction drive system 100 or on throttle 115.

In embodiments where gear motor 145 is a standard DC motor, motorcurrent draw may be proportional to normal force. Control unit 101 maydetermine (or estimate or lookup from a table) an amount of normal forceby monitoring the motor current draw. Accordingly, in some embodiments,it may not be necessary to monitor the position of gear motor 145 and/orworm gear 142. It may be possible to determine when worm gear 142 is atits maximum position by detecting a rapid increase in motor currentdraw. Furthermore, by monitoring the speed (or RPM) of the drive motor,it may be possible to determine when contact surface 109 disengages fromthe tire.

In view of the present disclosure, a person of skill in the art wouldunderstand that other mechanisms may be used to control the amount ofdepression into the tire and, thus, the amount of normal force. Forexample, rather than a pivoting mechanism, another embodiment couldemploy a linear motion mechanism that would enable motor mount assembly140 to move closer into tire 202 to increase normal force or away fromtire 202 to decrease normal force. Such a linear motion mechanism couldbe controlled and adjusted manually by the user or electromechanicallyby means of a linear actuator or similar.

In some embodiments, multiple traction modes may be established fordifferent road and/or weather conditions. For example, multiple tractionmodes may be provided in order of increasing (or decreasing) normalforce. A user may have the ability to select between two (or more)modes, one mode for dry conditions and another mode for wet conditions,a third (or even a fourth) mode may be provided for extremely slipperyconditions. Changing the traction mode (e.g., from “dry” to “wet”) maydecrease the value of angle θ₁ by a predetermined amount (e.g., by 5°)and thereby increase the normal force (and the amount of friction). Inembodiments of the disclosure, a user may select a traction mode byadjusting a knob disposed on drive assembly 103. Alternatively (or inaddition), a user may select a traction mode through a button (or otherinterface) disposed on a throttle mechanism or external controller, or auser may select a traction mode through an application running on theirsmartphone or other electronic device

In still other embodiments of the disclosure, an Automatic TractionControl System may adjust the value of angle θ₁ in response to sensedconditions, without requiring user selection of a traction mode. Asshown in FIG. 1B, in some embodiments, control unit 101 may includeAutomatic Traction Control System (“ATCS”) 150. ATCS 150 may beimplemented as software or firmware instructions executing on aprocessor within control unit 101, or as stand-alone circuitry.Alternatively, ATCS 150 may be provided within drive assembly 103,battery unit 102, or separately.

Automatic Traction Control System 150 may continuously vary the normalforce for optimal system performance, maintaining sufficient frictionbetween contact surface 109 and tire 102 to prevent slippage, while alsoimproving battery efficiency and reducing wear on tire 202. For example,ATCS 150 may quickly increase the normal force when slippage isdetected, until traction is regained between contact surface 109 andtire 202. ATCS 150 also may quickly reduce the normal force to maximizebattery efficiency. And ATCS 150 may completely disengage contactsurface 109 from tire 102 when motor 104 is not providing power toeliminate drag.

Automatic Traction Control System 150 may be particularly advantageouswhen used with the embodiment shown in FIG. 9, because worm gear 142 mayprovide fine control over angle θ₁ and the resulting normal force, aswell as significant mechanical advantages enabling high normal forces tobe applied with minimal physical effort. Moreover, knob 144 may allowthe user to manually calibrate ATCS 150 to provide more or less force,depending on the particular configuration and desired systemperformance.

In embodiments of the disclosure, Automatic Traction Control System 150may automatically increase the normal force (e.g., by decreasing angleθ₁) when slippage is detected. Slippage may be detected in a number ofways. For example, in embodiments of the disclosure, slippage may bedetected by comparing the speed of tire 202 (and/or wheel 201) to thespeed of contact surface 109. If the surface of tire 202 is moving at adifferent speed than contact surface 109 while the two are supposed tobe in contact, then Automatic Traction Control System 150 may determinethat slippage exists. In some embodiments, the speed of tire 202 may becalculated from the rotational speed of wheel 201; and the speed ofcontact surface 109 may be calculated from the rotational speed (orRPMs) of motor 104. Similarly, angular speeds (and/or other parameters)may be compared to detect slippage using known physical relationships.

In embodiments of the disclosure, a wheel speed sensor may sense thespeed of wheel 201 (and/or tire 202). For example, a sensor wheeldisposed on drive assembly 103 may continuously contact wheel 201(and/or tire 202) to detect the speed of wheel 201, which may bedirectly proportional to the speed of the unpowered sensor wheel. Asanother example, a sensor disposed on wheeled vehicle 200 and/or wheel201 may detect the wheel speed and send information wirelessly (e.g.,using Bluetooth) or over a wired connection to control unit 101 and/ortraction control system 150. In view of the present disclosure, a personof skill in the art would understand that wheel speed may be sensedand/or measured in various ways using sensors known in the art, such asOTS magnetic wheel speed sensors.

In still other embodiments of the disclosure, an optical sensor may beused to measure the ground speed, the ground speed may then be comparedto the speed of motor 104 to determine whether slippage exists (e.g.,using known relationships between speeds). Alternatively, ahigh-accuracy GPS sensor may be used to calculate the ground speed,rather than detecting the ground speed directly. The GPS sensor may beprovided in an attached (or synchronized) smartphone or other device orwithin friction drive system 100.

In yet other embodiments of the disclosure, a pressure sensor (and/orangular position sensor) may be disposed within pivot bracket 141(and/or pivot arm 107) to determine the pressure with which contactsurface 109 presses into tire 202, using known relationships betweenforces. During normal operation, when electrical power is supplied tomotor 104, contact surface 109 should press into tire 202; moreover,rotation of motor 104 and the friction force may act to pull motor 104towards the tire. The pressure between contact surface 109 and tire 202may be detected (or inferred) by measuring a corresponding pressurebetween pivot bracket 141 and stopping surface 146. If electrical poweris supplied to motor 104 and motor mount assembly 140 does not pull intotire 202 (thereby creating pressure between pivot bracket 141 andstopping surface 146), this may indicate that slippage is occurring.Thus, ATCS 150 may use the detected pressure (and/or angular position)together with motor current (and/or motor power or torque) to determinewhen slippage is occurring. Similarly, a pressure sensor disposed withinmotor mount assembly 140 could measure the pressure with which contactsurface 109 presses into tire 202.

In still other embodiments of the disclosure, an actual motor currentdraw may be compared with a desired motor current draw to deduce whenslippage exists. Desired motor current draw may be derived, at least inpart, from a throttle input from the user indicating the desire to powerwheeled vehicle 200. For example, the amount of desired current motordraw may be proportional to the amount of throttle depression, and themaximum throttle depression may correspond to a maximum current that maybe drawn by motor 104, adjusted for motor RPM. Alternatively, a morecomplex relationship may exist between desired motor current draw andone or more input signals (including those described above), and thisrelationship may be provided in the form of a lookup table or calculatedby ATCS 150 as needed. The calculation (or lookup) of desired motorcurrent draw also may take into account various physical properties ofmotor 104, including variation in motor current draw with motor speed.Once an amount of desired motor current motor draw is determined,Automatic Traction Control System 150 and/or control unit 101 mayattempt to deliver actual motor current equal to the amount of desiredmotor current. Then, actual motor current motor draw may be compared tothe amount of desired motor current draw to determine if slippageexists. For example, if actual motor current draw falls below the amountof desired motor current draw by a certain amount, this may indicatethat slippage exists, because motor 104 is not seeing a sufficient load.

In other embodiments, ATCS 150 may monitor the throttle level, RPMs ofmotor 104, current drawn by motor 104, and/or current drawn by gearmotor 145 in order to initialize engagement between contact surface 109and tire 202, detect when slippage exists, and/or automatically correctfor slippage. The exemplary control algorithms shown in FIGS. 10-18 maybe performed by ATCS 150 and/or control unit 101. FIGS. 10-18 aredescribed below with respect to the embodiment of friction drive system100 shown in FIG. 9, however, one of skill in the art in view of thepresent disclosure would understand how to modify the control algorithmsof FIGS. 10-18 to work with other embodiments of a friction drivesystem, including other embodiments described herein. For example, asdiscussed above, other mechanisms may be used to control the amount ofnormal force rather than a worm gear and a pivot bracket.

Automatic Traction Control System 150 may initialize pressure betweencontact surface 109 and tire 202. Friction drive system 100 may beconfigured to start with contact surface 109 disengaged from tire 202.For example, referring to the embodiment of FIG. 9, worm gear 142(controlled by gear motor 145) may return to a starting positionwhenever friction drive system 100 is powered down (or powered on). Inthe starting position, contact surface 109 may be positioned such thatit does not engage with tire 202 when mounted to a wheeled vehicle.Advantageously, returning to the starting position whenever frictiondrive system 100 is powered down may facilitate rapid removal andinstallation of friction drive system 100 from wheeled vehicle 200. Insome embodiments, worm gear 142 may retract off the tire whenever powerfrom motor 104 is not required (or desired), such as when the throttleis released for a period of time.

Current drawn by gear motor 145 may be used as an indicator of how muchnormal force exists between contact surface 109 and tire 202—as thenormal force increases, so does the current drawn by gear motor 145.Based on the direction in which worm gear 142 is advanced (e.g., in theforward direction), it may be possible to determine (or infer) whencontact is made with tire 202 (or other surface to be driven). Whencontact surface 109 is disengaged from tire 202, gear motor 145 may drawvery little current. Once contact surface 109 engages with tire 202,current drawn by gear motor 145 may rapidly increase. In someembodiments, current drawn by worm gear 145 may be proportional (or haveanother known relationship) to the amount of normal force betweencontact surface 109 and tire 202. Thus, the amount of normal force maybe controlled by regulating the current drawn by gear motor 145.Advantageously, the control algorithms shown in FIGS. 10-18 mayestablish sufficient normal force to engage tire 202 regardless of theexact placement of friction drive system 100 relative to tire 202 andregardless of the amount of air pressure in tire 202, because worm gear142 may continue advancing until the threshold level is reached (therebyindicating sufficient normal force).

FIG. 10A shows an exemplary flow diagram for a start-up orinitialization routine that may be used in embodiments of friction drivesystem 100, such as when starting with a throttle or Pedal Assist Sensor(“PAS”). In step 501, control unit 101 may initiate a start-up sequencewhen friction drive system 100 is turned on (e.g., by a switch or othermechanism) or in response to another indication. The start-up sequencealso may be selected based on the mode, such as throttle mode or PASmode, for example. In step 502, worm gear 142 may be advanced byapplying forward power to gear motor 145. Control unit 101 may monitorcurrent drawn by gear motor 145 and, in step 503, may determine when thecurrent draw exceeds a threshold value. If the current drawn by gearmotor 145 is below the threshold, then the flow may return to step 502and worm gear 142 may be advanced further. If the current drawn by gearmotor 145 is above the threshold, then the flow may proceed to step 504and worm gear 142 may be retracted by a preset amount, for example, byapplying reverse power to gear motor 145 for a period of time or for apredetermined number of increments. The preset amount may be set suchthat contact surface 109 is positioned slightly off of tire 202 but caneasily be engaged by advancing worm gear 142. In step 505, control unit101 may wait for a signal to engage the tire, such as a signal from thethrottle or PAS.

In step 502 of FIG. 10A, control system 101 may vary the amount ofadvancement of worm gear 142 with the amount of current drawn by gearmotor 145; for example, the amount of advancement may decrease as theamount of current drawn increases, in order to rapidly approach thethreshold level. In this way, worm gear 142 initially may advancequickly to engage the tire and then more slowly as the tire is engagedand the threshold level is approached. This approach may be usedthroughout. FIGS. 10-17 whenever advancing worm gear 142 towards aposition of engagement

FIG. 10B shows another example of a flow diagram for a start-up orinitialization routine that may be used in embodiments of friction drivesystem 100, such as when starting with a throttle or Pedal Assist Sensor(“PAS”). In step 601, control unit 101 may initiate a start-up sequencewhen friction drive system 100 is turned on (e.g., by a power switch orother mechanism) or in response to another indication. The start-upsequence also may be selected based on the mode, such as throttle modeor PAS mode, for example in step 602, worm gear 142 may be advanced byapplying forward power to gear motor 145. Control unit 101 may monitorcurrent drawn by gear motor 145 and, in step 603, may determine when thecurrent draw exceeds a lower threshold value. If the current drawn bygear motor 145 is below the lower threshold, then the flow may return tostep 602 and worm gear 142 may be advanced further. If the current drawnby gear motor 145 is above the lower threshold, then the flow mayproceed to step 604 and the position of worm gear 142 may be recorded bycontrol unit 101 and stored in memory. For example, the position of wormgear 142 may be recorded as an angular position, a number ofrevolutions, a number of increments, a time period, or other measurementthat allows the position to be identified and repeated. In step 605,worm gear 142 may be advanced by applying forward power to gear motor145. In step 606, control unit 101 may determine if the current drawn bygear motor 145 exceeds an upper threshold. If the upper threshold is notexceeded, then worm gear 142 may return step 605 and further advanceworm gear 142. If the upper threshold is exceeded, then the flow mayproceed to step 607 and the position of worm gear 142 may again berecorded by control unit 101 and stored in memory. In step 608, wormgear 142 may be retracted to the position corresponding to the lowerthreshold by applying reverse power to gear motor 145 until the positionis reached. The position corresponding to the lower threshold may, forexample, be a position of minimum engagement between contact surface 109and tire 202. In step 609, worm gear 142 may be retracted by anadditional preset amount in order to disengage from tire 202. In step610, control unit 101 may wait for a signal to engage the tire, such asa signal from the throttle or PAS.

FIG. 11 shows an example of a flow diagram for a shut-down or resetroutine that may be used in embodiments of friction drive system 100. Instep 700, control unit 101 may wait for a signal to shut-down or reset,such as turning off a power switch or other indication. In step 701,worm gear 142 may be retracted by applying reverse power to gear motor145 until a position of maximum retraction has been reached. A positionof maximum retraction may be determined, for example, by monitoring acurrent drawn by gear motor 145. When the position of maximum retractionin the reverse direction is reached (e.g., when pivot bracket 141 cannotphysically move further) the current drawn by gear motor 145 may spikeand be detected by control unit 101. In step 702, control unit 101 maypower down friction drive system 100. In step 703, control unit 101 maywait for a power-on indication.

Embodiments of friction drive system 100 may include a “Tailwind” modethat simulates the effect of tailwind by providing constant power outputto drive motor 104 when contact surface 109 is engaged with tire 202.For example, Tailwind mode may be initiated once the wheeled vehiclereaches a certain minimum speed.

FIG. 12A shows an example of a flow diagram for a start-up orinitialization routine that may be used in Tailwind mode in embodimentsof friction drive system 100. In step 801, control unit 101 may initiatea start-up sequence when friction drive system 100 is turned on (e.g.,by a switch or other mechanism) or in response to another indication,such as switching to Tailwind mode. In step 802, worm gear 142 may beadvanced by applying forward power to gear motor 145. Control unit 101may monitor current drawn by gear motor 145 and, in step 803, maydetermine when the current draw exceeds a threshold value. If thecurrent drawn by gear motor 145 is below the threshold, then the flowmay return to step 802 and worm gear 142 may be advanced further. If thecurrent drawn by gear motor 145 is above the threshold, then the flowmay proceed to step 804 and wait for a signal. For example, control unit101 may wait for a signal that a certain speed has been reached and thendrive motor 104 may begin delivering power in Tailwind mode. Notably,contact surface 109 may remain engaged with tire 202 in step 804.

FIG. 12B shows another example of a flow diagram for a start-up orinitialization routine that may be used in Tailwind mode in embodimentsof friction drive system 100. In step 901, control unit 101 may initiatea start-up sequence when friction drive system 100 is turned on (e.g.,by a power switch or other mechanism) or in response to anotherindication, such as switching to Tailwind mode. In step 902, worm gear142 may be advanced by applying forward power to gear motor 145. Controlunit 101 may monitor current drawn by gear motor 145 and, in step 903,may determine when the current draw exceeds a lower threshold value. Ifthe current drawn by gear motor 145 is below the lower threshold, thenthe flow may return to step 902 and worm gear 142 may be advancedfurther. If the current drawn by gear motor 145 is above the lowerthreshold, then the flow may proceed to step 904 and the position ofworm gear 142 may be recorded by control unit 101 and stored in memory.In step 905, worm gear 142 may be advanced by applying forward power togear motor 145. In step 906, control unit 101 may determine if thecurrent drawn by gear motor 145 exceeds an upper threshold. If the upperthreshold is not exceeded, then worm gear 142 may return step 905 andfurther advance worm gear 142. If the upper threshold is exceeded, thenthe flow may proceed to step 907 and the position of worm gear 142 mayagain be recorded by control unit 101 and stored in memory. In step 908,worm gear 142 may be retracted to the position corresponding to thelower threshold by applying reverse power to gear motor 145 until theposition is reached. In step 909, control unit 101 may wait for asignal. For example, control unit 101 may wait for a signal that acertain speed has been reached and then drive motor 104 may begindelivering power in Tailwind mode. Notably, contact surface 109 mayremain engaged with tire 202 in step 909.

In embodiments of the disclosure, the actual current draw of drive motor104, the RPMs of drive motor 104, and the throttle input level may bemonitored at regular intervals (or continuously), and between about 1 to2 seconds of the most recent data may be stored in memory on a rollingbasis. ATCS 150 may use the throttle input level to lookup (orcalculate) a desired motor RPM value. For example, in some embodiments,the lookup table may be set such that the throttle input level as apercentage of maximum corresponds to motor RPMs as a percentage ofmaximum, when the system is in steady-state. The desired motor RPM valuemay be compared against the actual RPMs of drive motor 104 (as absolutevalues or percentages). If the desired motor RPM value is greater by apredetermined amount than the actual RPMs of drive motor 104, then thismay indicate that the user desires to accelerate and additional powermay be provided to drive motor 104.

FIG. 13 shows an example of a flow diagram for responding to a throttleinput signal that may be used in embodiments of friction drive system100. For example, the flow diagram in FIG. 13 may be executed after oneof the start-up routines of FIGS. 10A-B. In step 1000, control unit 101may wait for a throttle input signal, for example, generated in responseto a user pressing the throttle. In step 1001, control unit 101 maycheck if the throttle input signal is below a minimum value, min. Ifbelow min, the flow may return to step 1002 and continue checking thethrottle input signal. If above min, the flow may proceed to step 1002and contact surface 109 may be engaged with tire 202. If start-uproutine 10A or 10B has already been executed, then the distance betweencontact surface 109 and tire 202 may be slight, such that engagement mayoccur rapidly. In step 1003, the wheel speed (or RPM) may be measuredand optionally stored in memory. For example, the wheel speed may bedetermined from the speed of drive motor 104 (e.g., using knownrelationships) while in an unpowered state.

In step 1004 of FIG. 13, control unit 101 may check that the wheel speed(or motor speed) is above a minimum speed for providing power when inthrottle mode (“Minimum Throttle Speed”). If the wheel speed is notgreater than the Minimum Throttle Speed, then the flow may return tostep 1003 and again measure the wheel speed. If the wheel speed isgreater than the Minimum Throttle Speed, then the flow may proceed tostep 1005 and electrical power may be provided to drive motor 104 suchthat the speed of contact surface 109 matches the speed of tire 202. Aswould be understood by a person of skill in the art in view of thepresent disclosure, the angular speeds (or RPMs) of contact surface 109and tire 202 would likely not match, since the diameter of contactsurface 109 will usually be much less than the diameter of tire 202;however, the tangential speeds of contact surface 109 and tire 202 wouldnormally be equal when the motor is engaged, assuming no slippage. Thus,the algorithm of FIG. 13 would likely use tangential speeds or anequivalent measurement.

Still referring to FIG. 13, in step 1006 power to motor 104 may beramped (e.g., increased or decreased) over time until a target valuecorresponding to the throttle input signal is reached. For example, thetarget value may be a speed, a motor torque, a motor power, or a motorcurrent; and the target value may be calculated, looked-up, or otherwisedetermined from the throttle input signal (and/or other parameters). Instep 1007, control unit 101 may check to determine if the throttle inputsignal is still above min if yes, then the flow returns to step 1006 andpower to the drive motor is provided to maintain the current targetvalue; the target value itself may vary over time based on the throttleinput signal. If the throttle input drops below min, then power to drivemotor 104 may be cut off in step 1008. In step 1009, contact surface 109may be disengaged from the tire before returning to step 1000 andwaiting for the throttle input signal. Step 1009 may occur after waitingfor a predetermined period of time, for example, 30 seconds or 1 minutein order to avoid repeated disengagement and reengagement. Inalternative embodiments, step 1009 may be skipped altogether and contactsurface 109 may remain engaged with tire 202.

FIG. 14 shows an example of a flow diagram for engaging a contactsurface of the drive motor (or roller) that may be used in embodimentsof friction drive system 100. For example, the algorithm of FIG. 14 maybe used to perform step 1002 of FIG. 13. In step 1101, a request may bereceived by software executing in control unit 101 to engage contactsurface 109 with tire 202 (described in FIG. 14 as a request to engage amotor or roller). In step 1102, worm gear 142 may be advanced by apredetermined amount, for example, by applying forward power to gearmotor 145. In step 1103, control unit 101 may compare the current drawof gear motor 145 to determine whether it exceeds a threshold value. Ifthe threshold is not exceeded, then the flow may return to step 1102 andagain advance worm gear 142. If the threshold is exceeded, then the flowmay proceed to step 1104, because contact surface 109 is now engagedwith tire 202 and drive motor 104 may begin delivering power.

In alternative embodiments, it also may be possible to determine whenengagement has occurred by monitoring the RPMs of drive motor 104 in anunpowered state: if the wheeled vehicle is in motion, then the motorRPMs will be greater than zero once engagement occurs.

Referring to step 1103 of FIG. 14, the threshold level of current drawnby gear motor 145 may be predetermined and/or preset to provide anoptimal amount of normal force (and, thus, friction) under normaloperating conditions (e.g., dry conditions on a paved road). In otherembodiments, the threshold level may be set dynamically based ondetected conditions, such as moisture on tire 202, motor RPMs, batterystate, and/or other parameters. In still other embodiments, thethreshold level may be determined, at least in part, based on a modeselected by the user (e.g., “Tailwind”, “High Traction”, “Low Traction”,etc.). In yet other embodiments, the threshold level may be set duringthe initialization process, for example, a certain amount between theminimum and maximum recorded values. It also may be possible to commandworm gear 142 to a predetermined position (or a position set duringinitialization) without (or in addition to) monitoring current drawn bygear motor 145 (e.g., instead of step 1103).

FIG. 15 shows an example of a flow diagram for disengaging contactsurface 109 of drive motor 104 (or a roller) that may be used inembodiments of friction drive system 100. For example, the algorithm ofFIG. 15 may be used to perform step 1009 of FIG. 13; in step 1008 ofFIG. 13, power to drive motor 104 may be cut before beginning the flowof FIG. 15. In step 1201 of FIG. 15, a request may be received bysoftware executing in control unit 101 to disengage contact surface 109from tire 202 (described in FIG. 15 as a request to disengage a motor orroller). In step 1202, worm gear 142 may be retracted by a predeterminedamount, for example, by applying forward power to gear motor 145. Instep 1203, control unit 101 may measure the RPM of drive motor 104 (whenit is unpowered) to determine whether it exceeds zero. If the drivemotor RPM is not zero, this indicates that disengagement has notoccurred because the motor is still being spun by the wheel. In thiscase, the flow returns to step 1202 and worm gear 142 may be furtherretracted. If the motor RPM is zero, then the flow may proceed to step1204, because disengagement has occurred.

FIG. 16 shows an example of a flow diagram for automatically detectingand correcting slippage that may be used in embodiments of frictiondrive system 100. In step 1300, ATCS 150 (and/or control unit 101) mayinitiate traction control. For example, traction control may beinitiated a predetermined time after engagement with the tire, asdescribed in FIG. 14, or immediately after initiating Tailwind mode, asdescribed in FIGS. 12A and 12B. Alternatively, in some embodiments,traction control may be initiated above a certain speed when the motoris engaged and providing power. In step 1301, ATCS 150 may measure theRPM of drive motor 104 (“motor RPM”). Alternatively (or in addition),the motor RPM may be provided to ATCS 150 by external software,circuitry, and/or sensors. The motor RPM may be stored in memory. Instep 1302, a ratio of current motor RPM to a prior stored value of motorRPM may be generated and compared to a threshold value. In the firstiteration of the loop, when there is no prior motor RPM value stored,motor RPM may be compared to itself or the comparison may be skipped andanother value measured upon returning to step 1301, for example.

In step 1302, if the ratio of current motor RPM to prior motor RPM (“RPMratio”) exceeds a certain threshold (optionally, expressed as apercentage) for a given logic loop delay time, then it may be possibleto deduce that slippage has occurred. This is true because motor RPMnormally should not increase above a certain rate when contact surface109 is engaged with tire 202, due to realistic acceleration limitsdetermined by motor power output and typical weight of rider and bike orscooter. Thus, in effect, the threshold value of the RPM ratio sampledover a given period of time may represent a maximum allowed accelerationof drive motor 104 and wheeled vehicle 200 which friction drive system100 is installed on. For example, in embodiments with a software loopperiod of 20 ms, a threshold value of 1.01 may be used to indicate thatslippage has occurred, as this rate of change of RPM would indicate a50% increase in RPM per second, likely exceeding realistic accelerationexpectations for the given power and weight.

If the RPM ratio is below the threshold, then the flow may return tostep 1301 and again measure the motor RPM. If the RPM ratio exceeds thethreshold, then the flow may proceed to step 1302 and ATCS 150 mayreduce (including up to cutting completely) power to drive motor 104. Instep 1304, the normal force between contact surface 109 and tire 202 maybe increased by a preset amount, for example, by applying forward powerto gear motor 145 for a certain amount of time, increments, degrees, orrotations. In step 1305, ATCS 150 may wait for the motor RPM to returnto a prior value (e.g., before the acceleration spike), which mayindicate that slippage has stopped. In many cases, it should take nomore than about 0.5 seconds from reducing (or cutting) power to drivemotor 104 in step 1303 for the motor RPM to return to a prior value.Once the motor RPM returns to a prior value, indicating that slippagehas likely stopped, power may be restored to drive motor 104 in step1306 and the flow may return to step 1301.

In alternative embodiments of a slippage detection loop, in step 1305,ATCS 150 may wait a predetermined amount of time, such as 0.2 to 0.5seconds, before restoring power to drive motor 104 in step 1306. Instill other embodiments of a slippage detection loop, in step 1305, awheel speed may be detected, and ATCS 150 may wait for the motor speedto equal the wheel speed (indicating that slippage has stopped) beforerestoring power to drive motor 104 in step 1306.

FIG. 17 shows another example of a flow diagram for automaticallydetecting and correcting slippage that may be used in embodiments offriction drive system 100. In step 1400, ATCS 150 (and/or control unit101) may initiate traction control. For example, traction control may beinitiated a predetermined time after engagement with the tire, asdescribed in FIG. 14, or immediately after initiating Tailwind mode, asdescribed in FIGS. 12A and 12B. Alternatively, in some embodiments,traction control may be initiated above a certain speed when the motoris engaged and providing power. In step 1401, ATCS 150 may measure themotor RPM. Alternatively (or in addition), the motor RPM may be providedto ATCS 150 by external software, circuitry, and/or sensors. The motorRPM may be stored in memory. In step 1402, a ratio of current motor RPMto a prior stored value of motor RPM may be generated and compared to athreshold value. In the first iteration of the loop, when there is noprior motor RPM value stored, motor RPM may be compared to itself or thecomparison may be skipped and another value measured upon returning tostep 1401, for example. In step 1402, if the ratio of current motor RPMto prior motor RPM (“RPM ratio”) exceeds a certain threshold, then itmay be possible to deduce that slippage has occurred, as previouslydescribed with respect to step 1302 of FIG. 16.

If the RPM ratio does not exceed a certain threshold, then the normalforce may be decreased in step 1403, for example, by applying reversepower to gear motor 145 for a certain amount of time, increments,degrees, or rotations. If the RPM ratio exceeds the threshold, then theflow may proceed to step 1404 and power to drive motor 104 may bereduced (including up to cutting completely). In step 1405, the normalforce between contact surface 109 and tire 202 may be increased by apreset amount, for example, by applying forward power to gear motor 145for a certain amount of time, increments, degrees, or rotations. In step1406, ATCS 150 may wait for the motor RPM to return to a prior value(e.g., before the acceleration spike), which may indicate that slippagehas stopped. In many cases, it should take no more than about 0.5seconds from reducing (or cutting) power to drive motor 104 in step 1404for the motor RPM to return to a prior value. Once the motor RPM returnsto a prior value, indicating that slippage has likely stopped, power maybe restored to drive motor 104 in step 1407 and the flow may return tostep 1401.

Using the embodiment of FIG. 17, it may be possible to maintain thenormal force at an optimal level, such that a minimal amount of normalforce is applied without slippage. As one of skill in the art wouldunderstand in view of the present disclosure, hysteresis may be builtinto loop 1402, such that some amount of variation is tolerated in theRPM ratio before adjusting the amount of normal force.

FIG. 18 shows yet another example of a flow diagram for automaticallydetecting and correcting slippage that may be used in embodiments offriction drive system 100. In step 1500, ATCS 150 (and/or control unit101) may initiate traction control. For example, traction control may beinitiated a predetermined time after engagement with the tire, asdescribed in FIG. 14, or immediately after initiating Tailwind mode, asdescribed in FIGS. 12A and 12B. Alternatively, in some embodiments,traction control may be initiated above a certain speed when the motoris engaged and providing power. In step 1501, ATCS 150 may measure themotor RPM. Alternatively (or in addition), the motor RPM may be providedto ATCS 150 by external software, circuitry, and/or sensors. The motorRPM may be stored in memory. In step 1502, a ratio of current motor RPMto a prior stored value of motor RPM may be generated and compared to athreshold value. In the first iteration of the loop, when there is noprior motor RPM value stored, motor RPM may be compared to itself or thecomparison may be skipped and another value measured upon returning tostep 1501, for example. In step 1502, if the ratio of current motor RPMto prior motor RPM (“RPM ratio”) exceeds a certain threshold, then itmay be possible to deduce that slippage has occurred, as previouslydescribed with respect to step 1302 of FIG. 16.

In step 1502, if the RPM ratio does not exceed the threshold, then theflow may proceed to step 1503 and a “no-slip” counter may beincremented, for example, by 1. In step 1504, ATCS 150 may check if the“no-slip” counter is above a minimum threshold (e.g., 10). If not, thenthe flow may return to step 1501 and motor RPM may be measured again. Ifyes, then the flow may proceed to step 1505, where the normal force maybe decreased, for example, by applying reverse power to gear motor 145for a certain amount of time, increments, degrees, or rotations. In step1505, the “no-slip” counter also may be reset. The use of a “no-slip”counter provides a delay before decreasing the normal force, which mayprevent rapid changes to the normal force and increase consistency ofoperation.

If the RPM ratio exceeds the threshold, then the flow may proceed tostep 1506 and power to drive motor 104 may be cut (or reduced). In step1507, the normal force between contact surface 109 and tire 202 may beincreased by a preset amount, for example, by applying forward power togear motor 145 for a certain amount of time, increments, degrees, orrotations. In step 1508, ATCS 150 may wait for the motor RPM to returnto a prior value (e.g., before the acceleration spike), which mayindicate that slippage has stopped. In many cases, it should take nomore than about 0.5 seconds from cutting (or reducing) power to drivemotor 104 in step 1506 for the motor RPM to return to a prior value.Once the motor RPM returns to a prior value, indicating that slippagehas likely stopped, power may be restored to drive motor 104 in step1509 and the flow may return to step 1501.

Embodiments of friction drive system 100 described herein may useregenerative charging and/or braking to restore power to battery unit102 when wheeled vehicle 200 brakes. For example, by leaving contactsurface 109 engaged with tire 202 during braking, it may be possible togenerate a reverse current in drive motor 104 that may be used to powerrechargeable batteries in battery unit 102. In addition, because thesystem may control normal force independently from drive motor directionand torque, it may be possible to employ regenerative braking bysimultaneously reversing direction of drive motor 104 while alsoincreasing normal force, thereby applying high braking force to thewheel while regeneratively charging battery unit 102. Such aregenerative braking system also may offer the safety benefit of asecondary braking system for the bicycle or scooter (or other wheeledvehicle) which friction drive system 100 is mounted on.

Embodiments of friction drive system 100 may include electricalcomponents for charging the battery, for powering lights, for chargingexternal devices, and for other purposes. These electrical componentsmay be provided within control unit 101, battery unit 102, driveassembly 103, case 120, and/or separately. For example, drive assembly103 may include lights powered by battery unit 102. As another example,case 120 may include one or more USB ports for powering (or charging)external devices (e.g., cell phones, lights, cameras, etc.) using powerfrom battery unit 102. As yet another example, battery unit 102 may ainclude plug (and associated circuitry) for connecting with a standardelectrical outlet to charge battery unit 102. Thus, friction drivesystem 100 (and/or battery unit 102) may be used as a portable powersupply capable of powering various electrical devices, both on and off awheeled vehicle.

Embodiments of friction drive system 100 also may include software forcollecting information and/or performing calculations related toperformance, diagnostics, and/or tracking and for outputting relatedinformation to a display (e.g., LCD or LED screen) disposed on frictiondrive system 100; alternatively or in addition, information may beoutput to an application (“APP”) running on an external device, such asa smartphone or computer, for processing and/or display there. Forexample, software running on a processor within control unit 100 may useinformation gathered from battery 102, drive assembly 103, and/orwheeled vehicle 200 to perform calculations and output the speed,battery charge, battery efficiency, and/or projected range (among otherthings) for display. A projected range may be continuously updated innear real-time as friction drive system 100 is used, based oninformation such as battery charge, distance traveled, vehicle speed,and/or motor speed.

In embodiments of the disclosure, software running on a processor withincontrol unit 100 (or elsewhere) also may control the mode and/orsettings of friction drive system 100 in response to a user input. Forexample, a user may operate a user interface (e.g., by pressing buttons)to select a traction mode, to set maximum power and/or speed limits, toset when the motor should begin delivering power, and/or to adjust othersettings. For example, a user may select to power motor 104 only when acertain threshold of vehicle (or pedal) speed is exceeded. In someembodiments, a user may select the traction mode—such as “dry” or“wet”—directly via the APP. As already explained, the APP also maydisplay information such as distance, location, battery power, batteryefficiency, projected range, and so forth. The APP may also storeinformation and display information over time and/or historicalperformance metrics.

In view of the present disclosure, a person of skill in the art wouldunderstand that embodiments described as engaging with a tire could bemodified to engage with other parts of the wheel, such as the rim. Aperson of skill in the art would also understand that embodiments inwhich a contact surface on the motor engages directly with the tire maybe modified such that a contact surface on one or more rollers—which maybe powered by the motor—engages with the tire or wheel; in this case,the motor may be enclosed within the casing. A person of skill in theart would also understand that embodiments described with respect tobicycles may be modified to work on other wheeled vehicles, such asscooters, skateboards, wheelchairs, and the like. A person of skill inthe art would also understand that embodiments described herein haveapplications beyond wheeled vehicles, including with motorcycles, remotecontrol vehicles, wind turbines, manufacturing systems, conveyor belts,railcars, trains, printers, toys and consumer devices, among otherdevices.

Advantages of embodiments of friction drive systems disclosed hereininclude, without limitation, the ability to add or remove electricfriction drive power to a standard non-electric bike or scooter inseconds, the ability to use electric friction drive on multiple bikesand/or scooters interchangeably (including with folding bikes and kickscooters), and the ability to carry spare electric friction drive powerin a briefcase or bag to be used whenever it is needed. In addition,embodiments of a friction drive system disclosed herein are portable andcan easily be taken with the user to prevent theft of valuable e-bikecomponents.

Other advantages of friction drive systems and control algorithmsdisclosed herein include the ability to automatically adjust the amountof friction delivered in order to prevent slippage and adjust forchanging conditions, which also may increase battery life and decreasetire wear. Other advantages disclosed herein include safer operation ofa friction drive system. For example, by turning off power to the drivemotor when slippage is detected, embodiments disclosed herein mayprevent the tire from suddenly reengaging (or catching) with the contactsurface. Other advantages disclosed herein include automatic and rapidengagement and disengagement of the contact surface with the tireon-demand.

Embodiments of friction drive systems disclosed herein may be used withbike share bicycles and, advantageously, may provide electric power to abike share bicycle without requiring the expense or complexity ofconventional electric bicycles, which typically require battery swapfunctionality and multi-battery docking stations for bike share use.Additionally, embodiments disclosed herein allow individuals to addelectric power to a bike share bicycle when it would otherwise not beavailable. This allows individuals to experience the benefits ofelectric bicycles including reduced effort, faster speed, and longerrange, while taking advantage of the benefits of a bike share program.Embodiments disclosed herein also allow bike share operators to benefitfrom increased membership due to the attractiveness of electric power toindividuals, and higher asset utilization of their bike share fleet, asthe higher speeds enabled by electric power shorten the time needed foran individual to complete a trip and allow the bike to be returned tothe dock and checked out by another user more quickly.

It should be understood that, while various embodiments have beendescribed herein, the claimed invention(s) should not be limited bythose embodiments. To the contrary, the foregoing summary, detaileddescription, figures, and abstract have been presented for illustrativepurposes, and are not meant to limit the claims. Indeed, as a person ofskill in the art in view of the present disclosure would recognize,various changes can be made to the embodiments described herein withoutdeparting from the scope and spirit of the present invention(s).

1. A friction drive system, comprising: a drive assembly comprising amotor and a contact surface capable of engaging with a tire of a wheeledvehicle, and a control unit comprising an automatic traction controlsystem, wherein the automatic traction control system is capable ofautomatically adjusting an amount of normal force between the contactsurface and the tire when the friction drive system is mounted to thewheeled vehicle.
 2. The friction drive system of claim 1, furthercomprising: a battery unit, wherein the control unit determines anamount of electrical current to deliver from the battery unit to themotor based at least in part on an input signal.
 3. The friction drivesystem of claim 2, wherein the control unit determines the amount ofelectrical current to deliver from the battery to the motor based atleast in part on a motor speed or a motor current draw.
 4. The frictiondrive system of claim 2, wherein the input signal is provided by atleast one of a throttle mechanism or a pedal assist sensor.
 5. Thefriction drive system of claim 2, wherein the automatic traction controlsystem is capable of reducing the delivery of electrical current fromthe battery unit to the motor when slippage is detected between thecontact surface and the tire.
 6. The friction drive system of claim 5,wherein slippage is detected by determining whether a speed of the motorhas increased by more than a maximum threshold value for a samplingperiod.
 7. The friction drive system of claim 5, wherein the automatictraction control system is capable of increasing the amount of normalforce after slippage is detected.
 8. The friction drive system of claim7, wherein the automatic traction control system is capable ofincreasing power to the motor after increasing the amount of normalforce such that slippage is no longer detected.
 9. The friction drivesystem of claim 1, wherein the drive assembly comprises a pivotmechanism, and wherein the automatic traction control system is capableof adjusting the amount of normal force by changing an angle of thepivot mechanism.
 10. The friction drive system of claim 9, wherein thepivot mechanism comprises a worm gear.
 11. The friction drive system ofclaim 10, wherein the automatic traction control system controls theangle of the pivot mechanism by powering the worm gear with a gearmotor.
 12. The friction drive system of claim 11, wherein the automatictraction control system monitors a current draw of the gear motor todetermine when the contact surface is disengaged from the tire.
 13. Thefriction drive system of claim 11, wherein the automatic tractioncontrol system monitors the revolutions of the worm gear to determinewhen the contact surface is disengaged from the tire.
 14. The frictiondrive system of claim 1, wherein the drive assembly comprises a linearadjustment mechanism, and wherein the automatic traction control systemis capable of adjusting the amount of normal force by changing aposition of the linear adjustment mechanism relative to the tire.
 15. Afriction drive system, comprising: a drive assembly comprising a motorand a pivot mechanism, wherein a contact surface is disposed on themotor, and the motor is attached to an end of the pivot mechanism; andan automatic traction control system capable of automatically adjustingan angle of the pivot mechanism in response to one or more sensedconditions.
 16. The friction drive system of claim 15, wherein the oneor more sensed conditions includes at least one of a motor speed, amotor current, a vehicle speed, or a GPS signal.
 17. The friction drivesystem of claim 15 further comprising a battery unit and a control unit,wherein the control unit determines an amount of electrical current todeliver from the battery unit to the motor.
 18. The friction drivesystem of claim 15, wherein the pivot mechanism comprises a worm gearand a gear motor.
 19. The friction drive system of claim 18, wherein theautomatic traction control system adjusts the angle of the pivotmechanism by powering the worm gear with the gear motor.
 20. A frictiondrive system, comprising: a battery unit capable of delivering power toa drive assembly, wherein the drive assembly comprises a motor and acontact surface; and means for automatically controlling an amount ofnormal force delivered by the contact surface in response to one or moresensed conditions.
 21. The friction drive system of claim 20, whereinthe drive assembly further comprises a pivot mechanism and the contactsurface is disposed on a rotating mechanism attached to the pivotmechanism, wherein the rotating mechanism is powered by the motor. 22.The friction drive system of claim 21, wherein the means forautomatically controlling the normal force is capable of controlling anangle of the pivot mechanism.
 23. The friction drive system of claim 22,wherein the one or more sensed conditions includes at least one of amotor speed, a motor current, a vehicle speed, or a GPS signal.
 24. Amethod for automatic traction control in a friction drive systemcomprising the steps of: adjusting the position of an engagementmechanism by powering a gear motor until a current drawn by the gearmotor exceeds a threshold value; detecting a first speed of a drivemotor connected to the engagement mechanism when the drive motor isunpowered; applying power to the drive motor such that a second speed ofthe drive motor matches the detected first speed of the unpowered drivemotor; increasing the power to the drive motor until the drive motorreaches a third speed determined at least in part from an input signal;reducing power to the drive motor when a rate of change of drive motorspeed exceeds a threshold value.
 25. The method for automatic tractioncontrol in a friction drive system of claim 24, further comprising thestep of adjusting the position of the engagement mechanism such that thecurrent drawn by the gear motor increases.
 26. The method for automatictraction control in a friction drive system of claim 25, furthercomprising the step of increasing power to the drive motor.
 27. Themethod for automatic traction control in a friction drive system ofclaim 26, wherein the rate of change of drive motor speed is determinedfrom a ratio of a current drive motor speed to a previous drive motorspeed.
 28. The method for automatic traction control in a friction drivesystem of claim 27, wherein the engagement mechanism comprises at leastone of a pivot mechanism or a linear adjustment mechanism.
 29. Themethod for automatic traction control in a friction drive system ofclaim 24, wherein the input signal comprises information from at leastone of a throttle mechanism or a pedal assist sensor.
 30. The method forautomatic traction control in a friction drive system of claim 24,wherein the input signal comprises at least one of a motor speed, amotor current, a vehicle speed, or a GPS signal.